Macrocyclic structurally homoconjugated oligoacetylenes: Acetylene- and diacetylene-expanded cycloalkanes and rotanes

There is ample evidence for the significance of modern acetylene chemistry and its role for the future development in several areas of organic chemist ry. In this chapter, the successful syntheses and attempted approaches to m acrocyclic structurally homoconjugated oligoacetylenes and oligodiacetylene s, as well as some of their physical properties, are discussed. Such compou nds, which are formally derived from permethylated cycloalkanes by insertio n of -C=C- or -C=C-C=C- fragments between each pair of adjacent sp(3)-hybri dized carbon atoms, have been termed [n]pericyclines and expanded [n]pericy clines, respectively. These and analogous hydrocarbons formally derived fro m [n] rotanes (perspirocyclopropanated [n]pericyclines and "exploded" [n]ro tanes) as well as heteroanalogues of [n]pericyclines are presented. In addi tion, the preparations and properties of macrocycles with mixed ethyne and butadiyne expanders as well as the attempted syntheses of perspirocycloprop anated "exploded" [n]rotanes are also covered. In view of the reported prop erties, the question of cyclic homoconjugation and homoaromaticity in these unconventional compounds is discussed. Finally, some chemical transformati ons of these macrocyclic oligoacetylenes and oligodiacetylenes, e.g. the co nversion of diacetylene-expanded [n]rotanes into crowns of thiophenes, are presented.